Environmental Engineering Reference
In-Depth Information
14.3 Potential prolonged volcanic perturbations to the Earth system
As described above there is no evidence as yet that individual large explosive
eruptions cause signi
cant prolonged perturbations to the Earth system when
considered on typical geological timescales. However, some periods of geological
history are characterised by significant deviations from
'
background
'
volcanic
behaviour. These may result from some con
guration of factors within the planet
'
s
interior causing a fundamental change in the rate or nature of volcanism, or may be
a response to feedbacks with surface processes. We shall consider four ways that
deviations from
cantly affect the Earth
system on geological timescales: (i) temporal clustering of individual explosive
eruptions; (ii) long-term persistently elevated rates of volcanism originating from
deep in the planet
'
s interior, namely LIP volcanism; (iii) changes in rates and/or
style of volcanism in response to direct feedbacks from the surface environment;
and (iv) systematic and signi
'
background
'
volcanic activity might signi
cant perturbations to the magma volatile load and
composition of the gases emitted by volcanism.
(i) Temporal clustering of individual explosive eruptions
Although we can estimate recurrence times from the geological record for explosive
eruptions of different magnitudes these values are just averages, and the stochastic
nature of volcanic activity means that explosive eruptions and stratospheric SO
2
inputs may cluster purely by chance. For example, Miller
et al
.(
2012
)suggestthat
decadally-paced explosive volcanism over a
50-year period and sea-ice/ocean
feedbacks might be linked to the onset of the Little Ice Age (
~
1850).
In some tectonic settings, there is also evidence for clusters of large-magnitude
explosive eruptions of silicic magma that together form large-scale silicic
~
AD 1350
-
'
are
ups
'
. Prominent examples include the Altiplano
-
Puna complex of the central
Andes (10
-
1 Ma; de Silva and Grosnold,
2007
), and the Southern Rocky Mountain
volcanic
field of Colorado and New Mexico (38
-
23 Ma; Lipman,
2007
). These
'
are-ups
'
can be highly productive, with total volumes of erupted silicic magma
exceeding 10
4
km
3
(Altiplano
-
Puna), erupted at a time-averaged rate typically
10
-
2
km
3
/yr (de Silva and Gosnold,
2007
). From the records of known
large explosive eruptions, Mason
et al
.(
2004a
) identi
10
-
3
~
-
super-
eruptions
'
: from 36 to 25 Ma, and 13.5 Ma to present. During these periods,
the mean interval between M 8 and larger eruptions may have been dropped to
<
10
5
years. Even at this higher recurrence rate, the time-averaged SO
2
emissions
from Toba-scale events would be insigni
ed two pulses of
'
cant relative to background
uxes. To
date, only limited evidence has been found linking such
'
are-ups
'
to prolonged
cant perturbations to the Earth system (Cather
et al
.,
2009
).
and signi
